2009_Book_FoodChemistry

740 15 Cereals and Cereal Products
Fig. 15.53. Decrease in freezing water in the storage
of white bread. The bread was stored at room temperature
encapsulated to prevent drying (according to Slade,
Levine, 1991)
Fig. 15.55. Complex formation between monoacylglycerides
(MG) and amylose (1) or amylopectin (2)
(according to Knightly, 1977). x-axis: carbon number
of the saturated acyl residue. y-axis: tendency of
MG to form a complex with amylose or amylopectin
(mmole · 10 −2 MG/g polysaccharide)
Fig. 15.54. Rate of crystallization of B starch as a function
of temperature, (−•−•) formation of crystal nuclei,
(−◦−◦) crystal growth, (−×−×−) total crystal
formation (according to Slade, Levine, 1991)
The ageing process resulting from these events
reaches a maximum at ca. 14 ◦ C. As a result of
this course, the ageing of white-bread crumb
can be prevented by storage at <−5 ◦ C. But the
temperature must very quickly fall below the
critical temperature for nucleation.
Temperatures above 14 ◦ C also inhibit staling,
e. g., increasing the storage temperature from
21 to 35 ◦ C decreases the rate of amylopectin
retrogradation by a factor of 4 and improves
freshness of the crumb, but the aroma is dissipated.
Increased protein or pentosan content
slows retrogradation. A choice – actually a rule –
to extend the shelf life or freshness of the baked
product is the use of emulsifiers, such as mono-
acylglycerides or stearyl-2-lactylate. During
baking the emulsifier will be complexed with
both starch constituents, though to a different extents
(Fig. 15.55). Such complexes retard starch
retrogradation. Fewer carbohydrates can be
extracted from starch/monoacylglyceride adducts
than from starch alone. This effect probably
contributes to the increase in the cooking stability
of pasta after addition of monoacylglycerides
(cf. 15.5).
The staling of crumb is also delayed by bacterial
α-amylase. From amylopectin, this enzyme
cleaves branched oligosaccharides that consist
of 19–24 glucose units. Consequently, the formation
of crystalline structures in amylopectin is
hindered.
15.4.5 Bread Types
Only those bread types of significant economic
importance are listed in Table 15.63. Corresponding
data on chemical composition are given in Table
15.55.
Crisp bread (Knaeckebrot) and Pumpernickel are
special rye breads.